1. Field of the Invention
The present invention relates to a wide-angle compound-eye imaging device.
2. Description of the Related Art
A wide-angle compound-eye imaging device with a wide field of view is known in which light entering in a wide-angle capture range is collected by multiple optical lenses in predetermined divided or shared angular ranges in the direction from left to right in the wide field of view or wide-angle capture range (hereafter referred to simply as wide-angle direction), and unit images formed by the optical lenses in the respective angular ranges are combined into a wide-angle capture image as disclosed in e.g. Japanese Laid-open Patent Publication 2007-288569. In such compound-eye imaging device, the optical lenses are placed from left to right (left, center and right) in the wide-angle direction, while a prism is placed in front of each left and right optical lens to share each left and right angular range to bend a path of light entering in each left and right capture range. This allows that the optical lens used to share each left, center and right angular range has a capture range e.g. as small as 40° (degrees) so as to capture an image in a capture range of 120° (degrees) without distortion.
The compound-eye imaging device of this patent publication makes it possible to easily obtain a distortion-free wide-angle or panoramic image with a picture angle of maximum about 180° (degrees) from left to right in the wide-angle direction. However, the picture angle from up to down, which is in a direction perpendicular to the wide-angle direction, is limited by the capture angle (i.e. convergence angle) specific to each optical lens. For example, if each optical lens used has a specific capture angle of 40°, it is only possible to obtain an image with a picture angle as small as 40° from up to down in the direction perpendicular to the wide-angle direction. Note here that it is generally understood that the maximum allowable limit of the picture angle of an image to be captured by one optical lens without distortion is about 60°.
Thus, in order to allow each of the optical lenses to have a specific capture angle larger than 60° (degrees), each optical lens is required to be formed of a combined lens consisting of two or more lenses. However, in a compound-eye imaging device, each optical lens is normally formed very small (as small as a few millimeters, for example), so that the provision of the combined lens makes it difficult to manufacture the compound-eye imaging device, and increases its cost. If, on the other hand, each optical lens is formed large, the size or volume of the resultant compound-eye imaging device becomes large. This reduces the advantage of small size which the compound-eye imaging device basically has.
Besides, another compound-eye imaging device is known in which multiple optical lenses are used to form each unit image so as to allow respective unit images to be those with different picture angles as disclosed in e.g. Japanese Laid-open Patent Publication 2005-338505. However, this does not solve the problems described above.